Method of casting and rapid analysis of alloys



g- 19, 1947- s. M. BOUTON ET AL 2,425,725

METHOD bf CASTING AND RAPID ANALY5I$ 0F ALLOYS Filed Aug. 26, 1941*c4000 \rarnssm 11,0 on 4 cnwnlu' ammo: ur soummv a u aoumv 5 EEI-SCHUMAOIER Patented Aug. 19, 1947 METHOD OF CASTING AND RAPID 1ANALYSIS OF ALLOYS George M. Bouton, Madison, and Earle E. Schumacher,Maplewood, N. J., assignors to Bell Telephone Laboratories,Incorporated, New York, N. Y., a corporation of New York ApplicationAugust 26, 1941, Serial No. 408,314

4 Claims. (01. 22 -214) objectisto provide processes and means foraccomplishing a determination of the calcium content with the necessaryaccuracy and with sufllcient rapidity that the control may be exercisedin a commercially feasible and economically advantageous manner. v a

The invention is based, in part, upon the ,discovery that the per centof calcium in leadcalcium alloys may be estimated within close limitsof. accuracy by visual inspection and, in part, that the eflicacy ofthis visual method of estimation depends upon casting the ingots usedfor estimation in a controlled atmosphere, more specifically, anatmosphere in which the percentage of carbon dioxide and the relativehumidity or moisture content are controlled and regulated.

From a generic aspect the invention relates to a technique ofmetallurgical analysis by which ficial appearance. when cast in aparticular at-.

invention is exemplified in a process desirable for use in connectionwith a particular, form of lead-calcium cable sheath composed ofcommercial lead with a desired calcium content of 0.028 per cent plus orminus .005 per cent. For the particular purposes for which this cable isto be used this percentage of calcium gives the most desirablecombination of properties.

v Emphasis is laid upon the rapidity with which the method of thepresent specification may be performed; methods of the highest accuracywouldbe of very little use in calcium content control in industrialoperations wherein a continuous and reasonably rapid manufacture ofproducts is demanded because it is impractical to hold a kettle of alloymolten for a long time in order to await the calcium determination.

Thus in cable manufacture a method previously used consumed from one totwo hours from the time of taking samples until the reporting of theresult. This procedure was costly and, moreover, resulted in a lag incontrol so great that the calcium content of the finished product onsome mosphere, which is a function of the composition or the amount ofsome constituent therein;

' furthermore, by a regulated atmosphere is meant an atmosphere of whichthe constituents are regulated to the required degree which in the.

occasions fell outside the specified limits and caused a rejection ofcertain lengths of cable.

Since calcium is a very active element chem-,- ically, specialmanufacturing procedures have been developed to minimize the contact ofmolten lead-calcium alloy with the air. Despite the improved techniques,some calcium is always lost andmust be replaced. Before this can beaccomplished satisfactorily, obviously, the calcium content of the alloymust be determined. Conventional chemical procedures are accurate butunsatisfactory for plant control use because they are time consuming andtoo costly. The best of the chemical methods introduces a lag of atleast two hours in control of the contents of the lead melting kettle.Quantitative spectrographic analysis methods were carefully tested, andwhile they showed some advantage over conventional analyses, they werestill unduly time consuming.

an extent that their variations are much smaller than the variations ofnatural air as found in rooms and outdoor places; this specification andappended claims are to be read in the light of these considerations'This need for control has been manifest during some ten or twelve yearsof use of leadcalcium alloys for cable sheath. See Dean Patent1,890,013, dated December 6, 1932, on application filed June 29, 1928.With the increasing usage in lead-calcium alloys for cable sheath,storagebattery grids, and other applications, the need In a specificembodiment as applied herein the for a p rel a d not o c y metho fordetermining the calcium content has been urgent. In approaching theproblem, several methods involving physical, chemical, or electricalproperties of lead-calcium alloys were investigated. These methodsproved inadequate. Either the properties involved were insufiicientlysensitive to changes in calcium content, or other factors masked theeffect of calcium variations.

The more specific aspect of the present invention is related to theobservation that molten lead alloys containing calcium in the range overa few hundredths of a per cent quickly film over with an oxide coating.Observation of the characteristics of these molten alloys revealed nophenomena that varied sufliciently with calcium content to serve as aclue to the composition. When such alloys are chill cast with as littleagitation as possible, the surface of the ingots becomes progressivelyduller with increasing calcium content to a certain value. Furtherincrease in calcium content results in the fissuring of the surfaceoxide leaving bright metallic areas exposed. This fissuring phenomenonis the basis of the composition-sensitive indication employed forpresent purposes. When samples of lead-calcium are melted and cast underproperly controlled conditions the surface markings for a particularcomposition are reproduced with considerable fidelity in respect toareas of dull and bright surface. The ratio of these areas is dependenton the calcium content.

The conditions found necessary or desirable are, first, the molten testsample is exposed to the open atmosphere for the least possible time; asecond, the alloy should not be stirred nor the crucible shaken to anysubstantial extent during the casting operation; third, the heat isremoved from the crucible quicky after the last portion of the samplehas melted; fourth, the atmosphere of the casting chamber must becontrolled as to its carbon dioxide content and moisture content.

Further explanation has reference to the following drawings in which:

Figs. 1, 2, 3, 4 and represent as nearly as we have been able torepresent in drawings the surface appearance of test ingots castaccording to the methods of the invention and containing essentiallypure lead with calcium in the respective amounts of 0.021 per cent,0.024 per cent, 0.026 per cent, 0.028 per cent and 0.030 per cent;

Fig. 6 represents a transparent walled casting chamber used to cast testingots; and

Fig. 7 represents diagrammatically the apparatus employed for supplyinga controlled atmosphere to the casting chamber of Fig. 6.

Control of the atmosphere over the surface of test castings has beenfound necessary to insure reproducible results. For this reason theCellophane enclosed casting chamber 1 with a wooden or other suitablefioorshown in Fig. 6 is used. There is a door 2 on the right-hand sidefor insertion of the cruicible 3 and a rubber inlet tube 4 on the leftfor supply of the gas mixture. The end 6 of the chamber may consist ofmetal or any other suitable material, as may all of the chamber except atransparent window. Door 2 duced in metered quantities to the airpassing into the casting chamber. By means of appropriate flow meters,dry air could be mixed in definite proportions with air saturated withmoisture to produce the desired humidity. Another and perhaps simplersystem is to pass the dry air over salt or other solutions of knownvapor pressure. Carbon dioxide is conveniently made available by placingsolid carbon dioxide (dry ice) in a Dewar flask having a stopper withtwo exit tubes. By means of an escape valve on one tube any desired CO2pressure can be built up in the flask to force the gas through a flowmeter and into the air line leading to the casting chamber. Onesatisfactory arrangement of apparatus for controlling the composition ofthe atmosphere is diagrammed in Fig. 7.

. Fig. 7 with its applied legends is largely selfexplanatory. From asuitable air inlet of air supplied under pressure the air is dried overcalcium chloride, deprived of COz over anhydrous potassium. hydroxide,and humidified over a solution of vapor pressure known for thetemperature employed. Solid CO2 furnishes gas and an escape or releasevalve permits regulation of the tion, a melting and casting procedurefor the test may comprise flaps of non-combustible sheet material.

A tongs 5 may be employed to insert the crucible to pour a mass 1 ofmetal upon a metallic mold 8. This apparatus is quite simple and may Ibe quickly and conveniently constructed to pracspecimens is used whichresults in a minimum loss of calcium. Fluxes and inert atmospheres,which normally provide adequate protection against oxidation are. notused here because they interfere with the fissuring phenomenon that isthe basis of the method.

The procedure, in detail, comprises melting a piece of the cable sheathor other materiol to be ested in the,hemispherical sheet iron crucible 3which is about two inches in diameter. A Bunsen burner flame ofsufficient intensity to melt a 100 gram sample in two minutes is appliedto the crucible. The bottom edge of the sample melts first and thebalance of the sample slides smoothly into the pool of metal firstformed with a minimum of rupture of the surface. The broad round shapeof the crucible permits it to be tilted until the lip is but a fractionof an inch from the surface of the mold before the metal starts to pour,thus subjecting the stream of molten alloy to only a brief exposure tothe atmosphere during pouring. The molten alloy should never be stirrednor should the crucible be shaken unnecessarily during the castingoperation. Under the melting conditions described, the castingtemperature of the melt is controlled sufficiently if the crucible isremoved from the flame three or four seconds after the last portion ofthe sample has melted. By a slight modification of procedure, samplesfor analysis may be taken direct-- ly from commercial melting kettles.The shape or size of the mold used does not appear to be critical. Weuse an iron plate 1.9 cm. x 10 cm. x 20 cm. with a tapered depressionmilled in its surface. The test ingot is about 10 cm. long, 1.56

cm. wide and-0.06 cm. thick at the casting end and 0.95 cm. thick at theother end. It weighs to grams. The effect of mold temperature does notappear to be critical in the range from room temperature to that reachedby the mold pearance of chemically pure lead-calcium alloys cast in anatmosphere containing 0.02 per cent CO2 and of 50 per cent relativehumidity. In Fig.

of lead that is being used and be enabled to make 1 there are no darkareas and in Fig. 5 the dark areas are close to 50 per cent of thesurface. These dark areas in the actual specimens are actually verybright surfaces when viewed by-directly reflected light. Increasing thecarbon dioxide or decreasing the moisture'content causes the brightsurfaces to become more extensive and vice versa. This provides a fewthousandths of a per cent latitude in adjusting the sensitive range ofthe method to the median calcium content desired. To an extent alloyshaving calcium contents somewhat outside the range of the method may beestimated by admixture with known amounts of lead-calcium alloys ofknown calcium content. Pure lead, in general, cannot be used fordilution because the oxide and possibly traces of impurities present init cause the loss of some calcium from the mixture.

It has been found possible to make determinations by casting test piecesin open air and determining their content and then using these todetermine the calcium content of samples cast in air of similarcomposition. This method subjects one to the necessity of analyzing newtest pieces frequently but a more cogent difliculty resides in the factthat air, and particularly the carbondioxide and water vapor contentthereof, is or are subject to relatively great and irregular changesespecially in industrial locations. A change of 0.01 per cent in carbondioxide content will ordinarily produce a substantial change inindication. Control of atmospheres may be practiced in other ways thanby using a transparent substantially closed container as hereindescribed.

In the manufacture of lead-calcium cable the necessary adjustments inthe conditions of the test to compensate for the particular impuritiesand'amounts thereof which. are present.

Sumcient data have been collected in both laboratory and plant practiceto establish that the method here presented is rapid, reliable,

'and helpful for plant control application. It is also adequately exact.From a broad aspect the use of atmospheres in accordance with theinvention is not limited to the use of atmospheres containing only theusual constituents of the earth's atmosphere; these may be employed inproportions widely different thanin any atmosphere commonly found in theopen or in buildings; moreover, the presence of other artificiallyintroduced gases is not excluded, when these constituent when cast underan atmosphere of sheath as known to us to have been practiced, to

date only virgin chemical" lead has been employed. This grade of lead issubstantially free from As, Sn, Bi, Fe, Sb and Zn, and contains about0.004 per cent Ni, 0.06 per cent Cu and 0.007 per cent Ag. The variationin concentration of these elements in the supply of commercial lead ofthis type has not been found to be great enou'gh-to cause substantialinterference with the indications given by the casting test. However,the method is influenced by certain variations in impurity content which.are in excess of those normally encountered in the usual supply. Thepresence of tin to the extent of a few thousandths of one per centcauses low indications of calcium content. Th'euse of high purity leadin place of chemical lead has a similar effect. Bismuth additions up to0.1 per cent are inconsequential. Arsenic and antimony form compoundswith calcium which dross oil! in the mixing kettle so that theseelements would not be found in the finished sheath. Correction can bemade for -the effects of the interferin impurities referred to above,when their presence is known, by varying the atmosphere in the castingchamber, by admixture with a known proportion of alloy having apredetermined higher calcium content, or by a special set of test piecesof known calcium content and having the impurity to the same extent asthe material to be con- In factory operation affect the surfaceaccording to their proportion their proportion is controlled, carbontetrachlo ride is an example of such a substance which has been found toaffect the surface appearance but the control of which per so withoutcontrolling other constituents has not been found to be an accurateindicator for analytical purposes.-

As stated, tin affects the results, hence with the use oi known amountsof compositions of known calcium content as addition agents the methodcan serve for the control of tin content or detection of excess tincontent in lead used in factory operations.

What is claimed is:

l. The method of determining quantitatively the constituents of ametallic alloy of the type wherein variations of one constituent resultin.

significant changes in the exposed surface of samples of the alloy withvarious ranges of said known and definite composition, which comprises,firstcasting a standard series of samples of alloys containing knowndifferent amounts of the one constituent under said definite knownatmosphere, and casting a sample of the alloy, of which the amount ofsaid one constituent is to be determined, under an identical atmosphereand under similar conditions and arranging said sample and saidstandards for comparison of its exposed surface with the exposedsurfaces 'of the standard series of sample.

2. The method of determining the calcium content of a lead-calcium alloywhich comprises casting the alloy in a definite atmosphere containingconstituents which act upon the surface of the alloyduring cooling andarranging said casting for comparison of the surfae thereof with thesurfaces of castings of lead-calcium alloy having known calcium contentdetermined in another manner which are cast in a substantially identicalatmosphere whereby the calcium content of the casting may be determined.

3. The method of maintaining substantially at a single desired value thecalcium content of calcium-lead alloy articles which comprises takingsamples from different molten batches of said alloy, casting saidsamples under an atmosphere having the same fixed and known water vaporand carbon dioxide content, and altering the lead-calcium ratio in abatch that difiers in its surface characteristics from suchcharacteristics of a casting made under such an atmosphere and havingthe desired calcium content to produce an alloy (if the desiredcalciumcontent.

4. In the method of manufacturing a product comprising a lead-calciumalloy inwhich the ratio of calcium to lead is maintained at asubstantially constant value, the steps of taking successive samples ofthe molten alloy as it is produced and before it is used to make saidproduct, casting said samples under a fixed and constant artificialatmosphere of known water vapor and carbon dioxide content, and changingthe relative amount of one of the metallic constituents of the alloywhen the surface characteristics of a cast sample differ from thesurface characteristics of the alloy of said constant ratio cast underthe same atmosphere.

GEORGE M. BOUTON.

EARLE E. SCHUMACHER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date Gutherie et a1 Sept. 17, 1940Deitz et a1. Sept. 8, 1936 Yant et a] June 23, 1925 Gabriel Apr. 21,1925 Cushman 22, 1921 Mouneyrat 17, 1920 Bake 22, 1938 Bouton et a1.Feb. 10, 1942 OTHER REFERENCES (Copy in Div. 59.)

